This invention relates to devices for detecting and counting charged or ionizing particles passing into or through the device and more particularly relates to an amorphous silicon detector sensitive to any ionizing radiation such as electrons, x-rays, alpha particles, beta particles and gamma radiation.
Single crystal solid state detectors, especially those fabricated from silicon ang germanium, have enjoyed a long and productive history as radiation detectors. The single crystal restriction, unfortunately, results in high cost and limited sensitive area. If noncrystalline semiconductors could be made sufficiently sensitive to low levels of radiation, they would, for certain applications, circumvent the need for single crystals, and allow the easy manufacture of large area position sensitive sensors. Moreover, because they are already in a state of greater disorder, they could be expected to be considerably less senitive to radiation damage than their single crystal counterparts. Furthermore, in the case of amorphous silicon (a--Si) versus crystal silicon, a--Si has the advantage of being deposited on any type of substrate and also being deposited in multiple successive layers.
Recently, starting with the work of W. E. Spear et al in 1976, amorphous silicon (a--Si) growth with few defects has been possible the plasma decomposition of silane (SiH.sub.4) with an alteration of its conductivity by suitable doping such as PH.sub.3 and B.sub.2 H.sub.6 in the plasma assisted chemical vapor deposition process. This has lead to the extensive investigation of amorphous silicon in the research and development of photovoltaic or solar cells with intensive work to improve their conversion efficiency. Representative examples of amorphous silicon photovoltaic devices are found in U.S. Pat. No. 4,419,696 and 4,500,744 and also in Japanese publication No. 56-51880 published May 9, 1981. These devices are of the Schottky barrier type, p-i-n tpe and combination Schottky barrier and p-i-n type, respectively.
Recent advances in the fabrication of amorphous silicon devices, particularly in deposition techniques that produce layers with low trap densities, have encouraged us to investigate amorphous silicon as a ionizing particle detector.